This invention relates generally to separators, and more particularly to centrifugal separators of the self-powered type that can be used for removing contaminants from a liquid system such as the lubricating oil system of internal combustion engines.
In order to obtain long operating life for machinery such as internal combustion engines, it is extremely important to provide the highest level of filtration capacity and ability in the system to continually remove polluting materials such as particulates, as they become present or enter into the lubricating oil. Generally, these filters can be classified as one of two types, either full flow or bypass filters. In the full flow filter, a porous type filtering element is used, and it is placed directly between the oil pump and the remainder of the lubricating system so that all of the oil passes through the filter. Such filters generally tend to have filtering elements of relatively large porosity, not only because they must pass a relatively high volume of oil with a minimum of pressure drop across the filter, but also because as the contaminants are filtered out of the oil and remain on the filter element, they tend to reduce the size of the pores, which further limits the filtering action and increases the problems of rate of oil flow through the filter. With such full flow filters, it may be necessary to provide a bypass passage so that when the filter produces an excessive amount of restriction, oil flow is allowed to pass directly around the filter and such oil receives no filtering action whatever. Furthermore, because of the relatively large porosity of the filter elements, there are a number of fine-grained particulate materials which are not filtered out of the oil because they are too small to be retained on the filter element.
The other type of oil filter is the bypass type in which a certain amount of oil as it leaves the oil pump is diverted into a filter from which it returns to the oil sump to be recirculated through the oil pump without passing through the remainder of the lubricating system. While such bypass filters filter only a portion of the oil being pumped, they can be very efficient in terms of removing very small particulates because they operate under a high pressure drop between the supply pressure and the oil sump.
While bypass filters may be of the mechanical type having a porous filter element, centrifugal type filters are quite advantageously used in such applications. A typical such centrifugal filter is the one shown in Beazley U.S. Pat. No. 3,432,091, which includes a hollow casing within which is rotatably mounted a rotor element having an internal chamber and an outer wall. The casing is connected directly to the sump or drain, while high pressure oil is directed into the interior of the rotor. As the rotor fills with pressurized oil, the oil passes downwardly to a pair of diametrically located discharge orifices or jets having a restricted diameter. As the oil passes out through these orifices, it creates a reaction force which causes the rotor to spin within the housing, causing a centrifugal force on the wall of the rotor that attracts solid particles which then adhere to this wall both by centrifugal force when the rotor is rotating and by mechanical cohesion when the rotor stops whenever the machinery supplying the oil is stopped. As the oil is discharged from the orifices or jets, it undergoes a pressure drop from the high pressure within the rotor to what is substantially an atmospheric pressure within the housing from which it flows back to the oil sump. Because this type of filter allows high speed of rotation of the rotor, very high centrifugal forces can result, so that even very fine and lightweight contaminant particles can build up and be retained on the wall of the rotor. Generally, such filters have been the reusable type where the housing can be dismantled and a rotor removed and opened up so that the contaminants can be removed as a sludge from the interior, but it is also recognized that such filters may be made of a disposable type in which the entire unit is removed and replaced with a new one after a certain predetermined period of time. Such disposable filters have been shown in U.S. Pat. Nos. 4,106,689 and 4,165,032.
When centrifugal filters of this type function normally, they will remove a very high proportion of the contaminants and keep the lubricating oil from deteriorating. Thus, when such filters are used in motor vehicles having known duty conditions, it can easily be discovered that filter cleaning or replacement should be done at certain regular intervals, and if the filter has been functioning in its intended manner, there should be a predictable amount of accumulated sludge in the filter rotor. However, when such an inspection or cleaning is done and the expected amount of sludge is not found in the rotor, it must be assumed that the filter has not been functioning in the intended manner. This presumably results either from the rotor not reaching the intended operating speed of rotation or by the fact that perhaps at certain times the rotor was not even spinning at all. Malfunctions of this type have been known to occur from unexpected blockages of the supply line or damage to the rotor bearings, as well as possible clogging of the orifices. A more common cause of improper operation, however, has been found to result from improper drainage of the outer housing chamber or return line, which causes discharge oil to back up in the bottom of the filter. If this occurs, the lowest portion of the rotor, which may include the portions having the jet orifices, will become submerged in the excess oil and cause a frictional drag on the rotor that will greatly reduce its speed, and thereby virtually eliminate its filtering efficiency.
To overcome this problem, it has been recognized that it is necessary to provide an unrestricted drain line back to the sump, and while, ideally, this can be done by mounting the filter on the sump, this is usually not practical for most installations. As a result, installations where the filter is remote from the engine require the use of a relatively large diameter, and hence rather inflexible, hose connected between the bottom of the filter housing and the oil sump. Furthermore, the routing of this hose must be done quite carefully to avoid any possibility of sharp bends or complicated paths that could restrict the flow path. Additionally, care must be taken to avoid the possibility of getting an air bubble in the drain line, since it is recognized that under normal operating conditions, the air pressure within the outer housing should be equal to atmospheric pressure, and there is no positive pressure forcing the oil through the drain line.
One solution to this problem that has been used is to provide an atmospheric vent valve on the upper side of the outer housing to provide a bleed that would allow atmospheric air to enter the housing. However, such bleed must include a reverse flow check valve in case the internal housing does become pressurized because of an unanticipated blockage in the drain passages, which particularly may tend to happen when the engine is first started and the oil is relatively cold, and therefore of higher viscosity. Such check valve, however, can allow other contaminants to enter the filter from the exterior, and may, under some circumstances, permit the escape of oil.
Another proposed solution to the problem is that disclosed in U.S. Pat. No. 4,046,315, in which part of the incoming oil bypasses the centrifugal filter and is directed directly back to the sump through a jet pump arrangement below the housing. This jet pump is then intended to provide a positive dynamic pumping action in the cavity to positively remove oil that has accumulated therein and force it back to the sump. However, the jet pump oil is therefore not filtered, which lowers the efficiency of the filtering operation and may require the use of a higher capacity oil pump in the lubricating system of the internal combustion engine. Furthermore, such jet pumps may require a very small diameter jet orifice which is easily clogged, rendering the jet pump inoperative.